Antenna system and method for mitigating multi-path effect

ABSTRACT

An antenna system and method utilize a splitter electrically connectable to a single antenna for splitting an RF signal into two signals. A variable phase shifter shifts the phase of one of the signals. A combiner combines the phase shifted and non-phase shifted signals to produce a conditioned signal. A quality examiner circuit changes the amount of phase shift provided by the variable phase shifter to produce a plurality of different conditioned signals. The quality examiner circuit then determines a quality of each conditioned signal and changes the phase shift again to provide the highest quality conditioned signal to a receiver.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patentapplication Nos. 61/268,662, 61/268,663, 61/268,665, 61/268,673,61/268,674, and 61/268,689, each filed on Jun. 15, 2009 and each ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The application generally relates to a system and method for providing acombined antenna signal to a receiver.

2. Description of the Related Art

The use of radio frequency (RF) receivers in vehicles, such asautomobiles, is commonplace. In fact, many vehicles involve multiple RFreceivers for different applications. These applications include, butare not limited to, terrestrial AM radio broadcasts, terrestrial FMradio broadcasts, satellite radio broadcast (e.g., SDARS), globalposition system (GPS) reception, and cellular telephone reception.

One challenge in RF signal reception in vehicles is known as the“multi-path effect”. This effect occurs when an RF signal is reflectedoff of an object, thus causing a phasing delay. The object may be abuilding, a mountain, or the ionosphere. Because of this reflection anantenna may receive the RF signal at two different times, i.e., in twodifferent phases. The first phase may be received directly from thetransmitting source while the second phase may be received after the RFsignal is reflected off of the object. As such, the RF signal receivedby the antenna, and by the receiver, may be distorted.

As such, the subject disclosure provides an antenna system and method toovercome these and other deficiencies.

BRIEF SUMMARY AND ADVANTAGES

An antenna system for mitigating a multi-path effect on a radiofrequency (RF) signal received by a single antenna is disclosed herein.The system provides a conditioned signal to a receiver. A splitter iselectrically connectable to the antenna. The splitter splits the RFsignal received by the antenna into a first non-phase shifted signal anda second non-phase shifted signal. A variable phase shifter iselectrically connected to the splitter for receiving the secondnon-phase shifted signal. The phase shifter may phase shift the secondnon-phase shifted signal to produce a phase shifted signal. The systemalso includes a combiner having inputs electrically connected to thesplitter and the variable phase shifter. The combiner receives andcombines the first non-phase shifted signal and the phase shifted signalto produce the conditioned signal. A quality examiner circuit iselectrically connected to an output of the combiner. The qualityexaminer circuit receives the conditioned signal and determines aquality of the conditioned signal. The quality examiner circuitcommunicates with the variable phase shifter for changing an amount ofphase shift of the second non-phase shifted signal based on the qualityof the conditioned signal to modify the phase shifted signal to mitigatethe multi-path effect on the RF signal received by the antenna.

A method of conditioning an RF signal received by an antenna to mitigatea multi-path effect on the RF signal prior to providing a conditionedsignal to a receiver is also disclosed herein. The method includes thestep of splitting the RF signal received by the antenna into a firstnon-phase shifted signal and a second non-phase shifted signal. Thephase of the second non-phase shifted signal is shifted to produce afirst phase shifted signal. The first non-phase shifted signal and phaseshifted signal are combined to produce a first conditioned signal. Themethod further includes the steps of determining and recording a qualityof the first conditioned signal. The phase of the second non-phaseshifted signal is then shifted to produce a second phase shifted signaldifferent from the first phase shifted signal. The first non-phaseshifted signal and the second phase shifted signal are combined toproduce a second conditioned signal. The method also includesdetermining and recording a quality of the second conditioned signal.The quality of the first conditioned signal and the second conditionedsignal are compared to determine which of the conditioned signals has ahighest quality. The conditioned signal determined to have the highestquality is provided to the receiver.

By phase-shifting one branch of a split RF signal, then recombiningphase shifted and non-phase shifted signals, the system and methodmitigate a multi-path effect caused by reflections of the RF signal. Thesystem and method perform well utilizing an input from just a singleantenna and without numerous branch circuitry. As such, the system andmethod provides a cost effective technique to mitigate a multi-patheffect on the RF signal especially in comparison to standard antennadiversity schemes.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the disclosed subject matter will be readilyappreciated, as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

FIG. 1 is a block electrical schematic diagram of a first embodiment ofan antenna system;

FIG. 2 is a block electrical schematic diagram of a second embodiment ofthe system; and

FIG. 3 is a perspective view of a vehicle supporting an antenna for usewith the system and method.

DETAILED DESCRIPTION

Referring to the Figures, wherein like numerals indicate like partsthroughout the several views, an antenna system 10 and method is shownand described herein. The antenna system 10 and method are particularlyeffective for mitigating a multi-path effect on a radio frequency (RF)signal received by an antenna 12 and providing a conditioned signal to areceiver 14. However, those skilled in the art will realize otherfunctional applications for the system 10 and method described herein.Furthermore, the method described herein may be implemented with devicesother than those specific devices of the system 10.

In the illustrated embodiments, the system 10 and method are implementedin conjunction with a vehicle 16, such as an automobile, as shown inFIG. 3. However, it is appreciated that the system 10 and method may beimplemented in other types of vehicles as well as non-vehicleenvironments. The system 10 and method described herein function wellusing only a single antenna 12. That is, the system 10 and method do notrequire multiple antennas, nor an antenna array, to achieve superiorperformance. However, those skilled in the art realize that the system10 and method may alternatively be implemented with multiple antennas oran antenna array.

Referring now to FIGS. 1 and 2, an amplifier 17 may be electricallyconnected to the single antenna 12 for amplifying the RF signal receivedat the antenna 12. This amplifier 17 may be a low-noise amplifier (LNA)as is known to those skilled in the art. The amplifier 17 is preferablydisposed in close proximity to the antenna 12, or, alternatively, isdisposed somewhat distant from the antenna 12.

The system 10 includes a splitter 18 electrically connectable to theantenna 12. More specifically, in the illustrated embodiment, an inputof the splitter 18 is electrically connected to an output of theamplifier 17. The splitter 18 splits the RF signal received by theantenna 12 into a plurality of non-phase shifted signals. The splitter18 of the illustrated embodiments is implemented as a “two-waysplitter”, i.e., the splitter 18 includes one input (not numbered) andtwo outputs (not numbered). As such, the splitter 18 of the illustratedembodiments splits the RF signal into a first non-phase shifted signaland a second non-phase shifted signal. The splitter 18 in theillustrated embodiments does not shift the phase of the RF signals.Instead, the splitter 18 merely splits the RF signal into multiplesignals that are substantially identical to one another. However, inother embodiments (not shown), the splitter 18 may include more than twooutputs to produce other non-phase shifted signals.

The splitter 18 may be implemented as a Wilkinson power divider or othersuitable device. Preferably, the splitter 18 equally divides the powerof the RF signal between the outputs, such that each non-phase shiftedsignals have about the same power level. However, those skilled in theart will realize certain situations where it may be advantageous to havediffering power levels between the non-phase shifted signals.

The system 10 also includes a variable phase shifter 20 electricallyconnected to the splitter 18. More specifically, an input (not numbered)of the variable phase shifter 20 is electrically connected to one of theoutputs of the splitter 18. In the illustrated embodiments, the variablephase shifter 20 receives the second non-phase shifted signal from thesplitter 18 and may phase shift the second non-phase shifted signal toproduce a phase shifted signal. In the illustrated embodiments, theamount of phase shift imposed on the second non-phase shifted signal isvariable between 0 and 360 degrees. That is, the variable phase shifter20 may impose no phase shift on the second non-phase shifted signal,thus, not changing the non-phase shifted signal in any meaningful way.Or, the variable phase shifter 20 may impose any amount of phase shifton the non-phase shifted signal, based on the technical limitations ofthe specific variable phase shifter 20 that is implemented. For example,the variable phase shifter 20 may be capable of shifting the phase ofthe RF signal by 0° (no phase shift), 2.5°, 5°, 7.5°, 10°, 12.5°, and15°. Furthermore, those skilled in the art realize that the phase shiftof a signal is analogous to a time delay of the signal.

The system 10 also includes a combiner 22 for combining signals. Thecombiner 22 includes inputs (not numbered) electrically connected toboth the splitter 18 and the variable phase shifter 20. The combiner 22receives and combines the first non-phase shifted signal from thesplitter 18 and the phase shifted signal from the variable phase shifter20 to produce the conditioned signal.

The system further includes a quality examiner circuit 24. The qualityexaminer circuit 24 is electrically connected to an output (notnumbered) of the combiner 22 for receiving the conditioned signal. Thequality examiner circuit 24 determines a quality of the conditionedsignal and communicates with the variable phase shifter 20 for changingan amount of phase shift of the second non-phase shifted signal based onthe quality of the conditioned signal. Signal quality refers to any ofseveral aspects of a signal, including, but not limited to, high signalstrength, low noise in the signal, and high signal-to-noise ratio.

The quality examiner circuit 24 may be implemented as a microprocessor(not separately numbered) operating as a digital signal processor. Thoseskilled in the art realize numerous suitable microprocessors to beutilized as the quality examiner circuit 24. Furthermore, those skilledin the art realize other non-microprocessor implementations for thequality examiner circuit 24.

In a first embodiment of the system 10, as shown in FIG. 1, the qualityexaminer circuit 24 includes an input (not numbered) for receiving theconditioned signal and an output (not numbered) electrically connectableto the receiver 14 for providing the modified signal to the receiver 14.As such, the modified signal is passed through the quality examinercircuit 24. The quality examiner circuit 24 may further modify themodified signal with digital signal processing techniques as is realizedby those skilled in the art.

In a second embodiment of the system 10, as shown in FIG. 2, the outputof the combiner 22 is electrically connectable to the receiver 14 forproviding the conditioned signal to the receiver 14. As such, modifiedsignal is not passed through the quality examiner circuit 24, and is notfurther modified by the quality examiner circuit 24.

The system 10 may also include an analog-to-digital converter (ADC) 26.The ADC 26 is electrically connected to the combiner 22 and the qualityexaminer circuit 24 for receiving the conditioned signal from thecombiner 22 and providing a digital representation of the conditionedsignal to the quality examiner circuit 24. Use of the ADC 26 isespecially advantageous when either signal strength or noise are beingexamined as an aspect of signal quality. In the first embodiment, asshown in FIG. 1, the ADC 26 is integrated with the quality examinercircuit 24. In the second embodiment, as shown in FIG. 2, the ADC 26 isshown separate from the quality examiner circuit 24. Furthermore, thoseskilled in the art realize that the system 10 may be implemented withoutthe ADC 26.

As stated above, the method of conditioning the RF signal provides atechnique to mitigate a multi-path effect. The multi-path effect, asrealized by those skilled in the art, occurs when an RF signal isreflected off of an object, thus causing a delay. The object mayinclude, but is not limited to, a building, a mountain, and theionosphere. Because of this reflection, and subsequent delay, theantenna 12 may receive the RF signal in two different phases. The firstphase may be received directly from the transmitting source while thesecond phase may be received after the RF signal is reflected off of theobject.

Particularly, to determine the best combination of phase shifted andnon-phase shifted signals to make up the conditioned signal that isdelivered to the receiver 14, the conditioned signal is analyzed using aplurality of different phase shifts of the phase shifted signal. Thedifferent phase shifted signals may, for convenience, be referred to asa first phase shifted signal, a second phase shifted signal, a thirdphase shifted signal, and so on.

In the illustrated embodiments the quality examiner circuit 24 changesthe phase of the amount of phase shift provided by the variable phaseshifter 20. For each different amount of phase shift, the qualityexaminer circuit 24 analyzes the quality of the resulting conditionedsignal. The quality examiner circuit 24 then determines which of theresulting conditioned signals provides the highest quality signal andchanges to the phase shift of the variable phase shifter 20 to match thephase shift of the highest quality signal. The conditioned signal isthen provided to the receiver 14. Preferably, the quality examinercircuit 24 repeats this cycle only when needed, such as when the signalquality falls below a predetermined threshold. However, in otherembodiments, the quality examiner circuit 24 may repeat this cycle basedon other considerations.

In one particular example, the variable phase shifter 20 first producesa first phase shifted signal by phase shifting the second non-phaseshifted signal by a first amount. This first phase shifted signal iscombined with the first non-phase shifted signal to produce a firstconditioned signal. The quality examiner circuit 24 determines andrecords the quality of the first conditioned signal. The variable phaseshifter 20 then produces the second phase shifted signal by phaseshifting the second non-phase shifted signal by a second amount, whichis different than the first amount. As such, the second phase shiftedsignal is different from the first phase shifted signal. This secondphase shifted signal is combined with the first non-phase shifted signalto produce a second conditioned signal. Accordingly, the secondconditioned signal is different from the first conditioned signal. Thequality examiner circuit 24 determines and records the quality of thesecond conditioned signal. The quality examiner circuit 24 thendetermines which of the first or second conditioned signals provides thehighest quality signal and changes the phase shift of the variable phaseshifter 20 to match the phase shift of the highest quality signal.

Of course, the method may utilize more than a first and secondconditioned signal. For instance, the variable phase shifter 20 may alsoproduce a third phase shifted signal by phase shifting the secondnon-phase shifted signal by a third amount, which is different than thefirst and second amounts. As such, the third phase shifted signal isdifferent from the first and second phase shifted signals. This thirdphase shifted signal is combined with the first non-phase shifted signalto produce a third conditioned signal. Accordingly, the thirdconditioned signal is different from the first and second conditionedsignals. The quality examiner circuit 24 determines and records thequality of the third conditioned signal. The quality examiner circuit 24then determines which of the first, second, or third conditioned signalsprovides the highest quality signal and changes the phase shift of thevariable phase shifter 20 to match the phase shift of the highestquality signal.

Thus, the method provides a cost effective technique to mitigate amulti-path effect on the RF signal, especially in comparison to antennadiversity schemes, where multiple antennas are required. Accordingly,the system 10 also provides a cost effective technique to mitigate amulti-path effect on the RF signal when the quality examiner circuit 24is properly programmed to execute the method described herein.

The present invention has been described herein in an illustrativemanner, and it is to be understood that the terminology which has beenused is intended to be in the nature of words of description rather thanof limitation. Obviously, many modifications and variations of theinvention are possible in light of the above teachings. The inventionmay be practiced otherwise than as specifically described within thescope of the appended claims.

What is claimed is:
 1. A method of conditioning an RF signal received bya single antenna to mitigate a multi-path effect on the RF signal priorto providing a conditioned signal to a receiver, said method comprisingthe steps of: splitting the RF signal received by the single antennainto a first non-phase shifted signal and a second non-phase shiftedsignal; shifting the phase of the second non-phase shifted signal toproduce a first phase shifted signal; combining the first non-phaseshifted signal and phase shifted signal to produce a first conditionedsignal; determining and recording a quality of the first conditionedsignal; shifting the phase of the second non-phase shifted signal toproduce a second phase shifted signal different from the first phaseshifted signal; combining the first non-phase shifted signal and thesecond phase shifted signal to produce a second conditioned signal;determining and recording a quality of the second conditioned signal;comparing the quality of the first conditioned signal and the secondconditioned signal to determine which of the conditioned signals has ahighest quality; and providing the conditioned signal determined to havethe highest quality to the receiver.
 2. A method as set forth in claim 1further comprising the step of shifting the phase of the secondnon-phase shifted signal to produce a third phase shifted signaldifferent from the first and second phase shifted signals.
 3. A methodas set forth in claim 2 further comprising the step of combining thefirst non-phase shifted signal and the third phase shifted signal toproduce a third conditioned signal.
 4. A method as set forth in claim 3further comprising the step of determining and recording a quality ofthe third conditioned signal.
 5. A method as set forth in claim 4wherein said step of comparing the quality is further defined ascomparing the quality of the first, second, and third non-phase shiftedsignals to determine which of the conditioned signals has a highestquality.
 6. A method as set forth in claim 5 wherein said step ofproviding the conditioned signal is further defined as providing theconditioned signal determined to have the highest quality to thereceiver.
 7. A method as set forth in claim 6 wherein said step ofproviding the conditioned signal is further defined as shifting thephase of the second non-phase shifted signal to the phase shiftassociated with the conditioned signal having the highest quality.
 8. Amethod as set forth in claim 1 wherein said step of providing theconditioned signal is further defined as shifting the phase of thesecond non-phase shifted signal to the phase shift associated with theconditioned signal having the highest quality.